Mix the Dough: In a bowl, stir the masa harina and salt together. Slowly pour in the warm water while stirring with your hand. Mix until a cohesive dough forms.
Knead and Rest: Knead the dough inside the bowl for about 1 to 2 minutes. It should feel like soft playdough and not stick to your hands. Cover the bowl with a damp towel and let it rest for 15 minutes to fully hydrate.
Roll into Balls: Divide the dough into 12 equal pieces. Roll each piece into a smooth ball about the size of a golf ball. Keep them covered with the damp towel so they do not dry out.
Press Flat: Line a tortilla press (or the bottom of a heavy skillet) with two pieces of plastic cut from a zip-top bag. Place a dough ball in the center, close the press, and squeeze firmly to flatten it into a 15 cm circle.
Cook on the Skillet: Heat a cast-iron skillet or griddle over medium-high heat until hot. Peel the tortilla off the plastic and place it on the dry skillet.
Flip Twice: Cook the first side for 30 to 45 seconds until brown spots appear. Flip and cook the second side for about 1 minute. Flip it one last time—it should begin to puff up with steam.
Keep Warm: Transfer the cooked tortilla to a clean kitchen towel or tortilla warmer to keep it soft, pliable, and warm while you finish the rest.